title: Crystal structures of CusC review conformational changes accompanying folding and transmembrane channel formation.
abstract: Gram-negative bacteria, such as Escherichia coli, frequently utilize tripartite efflux complexes in the RND (resistance-nodulation-cell division) family to expel diverse toxic compounds from the cell. These complexes span both the inner and outer membranes of the bacterium via an α-helical, inner membrane transporter; a periplasmic membrane fusion protein; and a β-barrel, outer membrane channel. One such efflux system, CusCBA, is responsible for extruding biocidal Cu(I) and Ag(I) ions. To remove these toxic ions, the CusC outer membrane channel must form a β-barrel structural domain, which creates a pore and spans the entire outer membrane. We here report the crystal structures of wild-type CusC, as well as two CusC mutants, suggesting that the first N-terminal cysteine residue plays an important role in protein-membrane interactions and is critical for the insertion of this channel protein into the outer membrane. These structures provide insight into the mechanisms on CusC folding and transmembrane channel formation. It is found that the interactions between CusC and membrane may be crucial for controlling the opening and closing of this β-barrel, outer membrane channel.
authors.affiliation: Department of Chemistry, Department of Physics & Astronomy, Iowa State University, Ames, IA 50011, USA.
authors.forename: Hsiang-Ting
authors.initials: HT
authors.lastname: Lei
authors.affiliation: Department of Chemistry, Department of Physics & Astronomy, Iowa State University, Ames, IA 50011, USA.
authors.forename: Jani Reddy
authors.initials: JR
authors.lastname: Bolla
authors.affiliation: Department of Chemistry, Department of Physics & Astronomy, Iowa State University, Ames, IA 50011, USA.
authors.forename: Nicholas R
authors.initials: NR
authors.lastname: Bishop
authors.affiliation: Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA.
authors.forename: Chih-Chia
authors.initials: CC
authors.lastname: Su
authors.affiliation: Department of Chemistry, Department of Physics & Astronomy, Iowa State University, Ames, IA 50011, USA; Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA. Electronic address: ewyu@iastate.edu.
authors.forename: Edward W
authors.initials: EW
authors.lastname: Yu
mesh_terms: D018360:Crystallography, X-Ray; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D008958:Models, Molecular; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D017510:Protein Folding
chemical_list: C096350:CusC protein, E coli; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D050505:Mutant Proteins
keywords: 6-cyclohexyl-1-hexyl-β-d-maltoside; Cymal-6; DDM; PEG; heavy-metal resistance; n-dodecyl-β-d-maltoside; outer membrane channel; polyethylene glycol; resistance–nodulation–cell division; β-barrel membrane protein